1. Field of the Invention
The invention relates to a process for the surface treatment of semiconductor slices which effects, during a subsequent thermal treatment, the formation of centers with gettering capability by generating a mechanical stress field in at least one slice surface, and also relates to semiconductor slices polished on both sides obtainable thereby.
2. The Prior Art
In the production of electronic components made from semiconductor slices, the requirements imposed on the quality of the material used are constantly increasing due to the increasing integration density. In this connection, great importance is attached to an as fault-free, perfect crystal structure as possible. This applies, in particular, to the surface layer, which is relatively thin compared with the total slice thickness, on the front of the slice in which the actual construction of the circuits proceeds in the individual process steps. The point defects and/or agglomerations of point defects causing losses in yield have to be removed from this layer as completely as possible. For this purpose, the concept of rear-side gettering in which the point defects are extracted via the rear side of the slice has been successful.
In this connection, stacking faults and/or dislocation networks produced in the rear-side region in the interior of the slice are ultimately effective as gettering centers. For an optimum gettering action, these centers must not anneal out as a result of the various thermal processes at the manufacturing plant producing the component. They must not grow to the front side of the slice and they must not be removed by oxidation in the various oxidation steps either. Both for the stacking faults and also for the dislocation networks, the depth reached in each case ultimately depends on the processes carried out at the manufacturing plant producing the component.
In order to achieve a gettering action at the rear side of the slice, the latter is usually provided either with a coating composed of polycrystalline material or with a controlled surface destruction, usually known in technical language as "damage". Various "damage" methods are known. For example, damage methods include mechanical treatment processes associated with more or less severe material removal. In these damage processes the rear side of the slice is roughened by means of styli or sand jets (see U.S. Pat. No. 3,905,162), by means of a bath of fluidized abrasive grains (see German Offenlegungsschrift 2,927,220) or by means of moving carrier bodies having an elastic coating with abrasive grains bound therein (see German Offenlegungsschrift 3,148,957 or the corresponding U.S. Pat. No. 4,587,771) and thereby acquires a gettering action. A similar result can also be achieved with the method of the so-called "wet blasting" in which a pressurized water/abrasive grain spray jet acts on the rear side of the slice. The usually at least slightly roughened rear sides of the slices generated with these known processes may, however, result in an increased liberation of particles. These particles move to the opposite smooth surfaces during the processing steps at the manufacturing plant producing the component, which particles may reduce the yields of satisfactory components ultimately achieved.
The method of partially melting surface regions by means of a laser beam to generate a gettering rear side according to German Offenlegungsschrift 3,246,480 or the corresponding U.S. Pat. No. 4,539,050 is restricted to slices having a particular fine surface structure and can therefore be used only in specific cases.
Finally, German Offenlegungsschrift 2,537,464 or the corresponding U.S. Pat. No. 4,042,419 mentions, in addition to the possibility of generating a gettering action on the rear side by a slight grinding action, also discloses a method in which dopants are incorporated in the host lattice of the semiconductor up to their solubility limit at high temperatures. During the subsequent quenching to low temperatures, the dopant concentration exceeds this limiting value. This results in deformations and in the production of mismatched dislocations. In a subsequent polishing step, the damaged layer is then removed from the front side of the slice. This method is, however, time-consuming and, due to the high concentration of dopants present, is always associated with the risk of the contamination of the front side of the slice and/or of the apparatus used in the component production.